1. Field of the Invention
The present invention relates to a liquid crystal display panel, a liquid crystal display device, and a method of manufacturing the liquid crystal display panel.
2. Description of the Related Art
In recent years, liquid crystal display devices with liquid crystal display panel have been widespread use for, not only in relatively small information communication equipment such as a portable information terminal, but also in relatively large electric equipment such as a monitor. In particular, portable information terminals and the like employ a transflective liquid crystal display device that requires no backlight, aiming to reduce power consumption. Because a reflective liquid crystal display device uses outside light (e.g., sunlight) as light source, it is often difficult to recognize a display image in a dark room or the like. For this reason, transflective liquid crystal display devices having properties of both transmissive and reflective displays have been developed to enable the user to recognize a display image appropriately even in a dark room or the like as well as to reduce power consumption.
In such a transflective liquid crystal display device, a pixel has a transmission portion that light emitted from a backlight passes through, and a reflection portion that reflects outside light. With this configuration, the transflective liquid crystal display device can display an image by using a backlight and transmitting the light through the transmission portion of each pixel in case of a dark room or the like (a transmissive display mode), and can display an image by using outside light and reflecting the light at the reflection portion of each pixel in case of bright outside (a reflective display mode). The transflective liquid crystal display device with this configuration does not require the use of the backlight all the time, and thus is capable of reducing power consumption. For example, Japanese Patent Application Laid-open No. H8-292413 discloses a conventional transflective liquid crystal display device configured as above.
This conventional transflective liquid crystal display device enables color display both in the transmissive display mode and the reflective display mode. However, it has a trade-off that increasing the color sharpness in the transmissive display mode leads to a reduction in brightness in the reflective display mode, whereas increasing the brightness in the reflective display mode leads to a reduction in color sharpness in the transmissive display mode.
Transflective liquid crystal display devices capable of performing sharp color display in the transmissive display mode and also bright monochrome display in the reflective display mode have been developed, as, for example, disclosed in Japanese Patent Application Laid-open No. 2004-93670.
In this transflective liquid crystal display device, when a color filter is formed on a portion where no reflecting film is formed, and no color filter is formed on a reflecting film, a large thickness difference occurs between the reflecting film (e.g., 0.1 micrometer) and the color filter (e.g., 1 micrometer to 2 micrometers). This results in a relatively large step therebetween (a step that cannot be covered by a general flattening film). Such a step generated causes a relatively large variation in the thickness (Gap) of a liquid crystal layer present between electrodes on substrates. As a result, for example, when display properties are optimized in one of the transmissive display mode and the reflective display mode, properties such as a contrast ratio are degraded in the other display mode. When the thickness of the flattening film is increased beyond a general range to reduce the effects of the relatively large step, the following four problems may occur. First, the increased thickness of the flattening film causes difficulty in ensuring a uniform thickness of the flattening film itself, causing variation in image quality of a displayed image. Second, increasing the thickness of the flattening film, which generally has a thickness of about 2 micrometers to 3 micrometers, causes spacers (particle diameter: about 4 micrometers to 6 micrometers) having a relatively higher hardness than the flattening film to cut deeper into the flattening film. The deeper cut causes a variation in cell gap more likely, resulting in variation in driving voltage. Third, since the flattening film is generally made of acrylic resin, the increased ratio of acrylic resin increases the hygroscopic properties thereof, degrading the liquid crystal properties accordingly. Fourth, using an increased amount of the flattening film leads to an increase in cost and weight. Japanese Patent Application Laid-open No. 2004-93670 also discloses a transflective liquid crystal display device including a reflecting film with apertures that is formed on a color filter provided over an entire substrate, aiming to reduce the effects of the step. This transflective liquid crystal display device is not capable of achieving both monochrome display and color display in the reflective display mode.